Heretofore, when stenosis occurs in a vessel of a living body, such as a coronary artery, percutaneous transluminal angioplasty (PTA) is performed in which the stenosed portion in the vessel is expanded to improve the blood flow using a medical balloon catheter.
The site once stenosed, however, is known to have high possibility of restenosis or acute occlusion due to intimal dissection even after PTA. To prevent such acute occlusion or restenosis, a tubular shaped stent is implanted at the site following PTA. The stent is in a contracted state when introduced into a blood vessel, and subsequently expanded in diameter so as to be deployed at the intended site scaffolding the vessel wall from its inside.
The stent to be implanted in a blood vessel is inserted and transported to the intended site in the vessel by using a catheter having a balloon which can be dilated with expansion medium supplied thereto (balloon catheter). Specifically, the contracted stent is mounted onto the balloon provided at the distal portion of the catheter to be inserted into the blood vessel and transported to the intended site together with the balloon. With the balloon inflation by supplying the expansion medium into it, the stent is expanded in diameter, and consequently deployed at the intended site. The once expanded stent keeps its expanded state even after the balloon is deflated by removal of the expansion medium, thereby scaffolding the implanted site radially to allow fluid path for humor such as blood in the vessel lumen.
Implantation of the stent using the above-mentioned catheter follows the procedure below.
First, a guide wire previously inserted in a catheter is inserted into a blood vessel and advanced to pass through a stenosed portion in the blood vessel. Next, the catheter is inserted into the blood vessel with the guidance of the guide wire to position the balloon on which a stent is mounted to the stenosed portion where the stent is intended to be implant. After the balloon is positioned to the stenosed portion along with the stent, expansion medium is supplied to the balloon by using an indeflator or the like, via an expansion medium supplying channel provided in the catheter, to inflate the balloon so that the stent is expanded in diameter to expand the stenosed portion in the blood vessel. After the inflation of the balloon and the expansion of the stenosed portion in the blood vessel, the expansion medium in the balloon is removed to decompress and contract the balloon. At this time, the stent remaining expanded is disengaged from the contracted balloon and deployed at the stenosed portion in the blood vessel to scaffold the inner wall of the blood vessel. Finally, the catheter is removed from the body and stenting is completed.
Examples of catheters for applying the above-mentioned PTA include an over-the-wire type catheter in which a guide wire insertion lumen is formed throughout its entire length from its distal end to proximal end, and a monorail type catheter in which a guide wire insertion lumen is formed from the distal end to a middle portion of the catheter where a port is opened to draw out the guide wire.
Among these catheters, the over-the-wire type catheters are advantageous due to its operatability in passing through the stenosed site with the guide wire, because the guide wire insertion lumen is formed from the distal end to the proximal end of the catheter.
On the other hand, in the monorail type catheters wherein the guide wire runs through only from its distal end to its middle portion, the length of the guide wire contained in the catheter can be shorter than that of the over-the-wire type catheter. The monorail type catheter, therefore, has an advantage that the catheter can be easily exchanged without using an extension guide wire or an exchanging device to draw out the catheter, if the catheter needs to be removed leaving the guide wire behind in the vessel for insertion of another catheter.
Some procedures require a plurality of stents depending on size of the stenosed portion or the shape of blood vessel. In these cases, the catheter on which a stent is mounted needs to be replaced with another one to deploy another stent. To do this, the catheter has to be exchanged quickly with leaving the guide wire behind in the blood vessel. The monorail catheters to implant a stent allow quicker exchange of catheters and efficient implantation of multiple stents. Examples of this kind of monorail type balloon catheters are disclosed in Patent Document 1 and 2.
When implanting a stent into a blood vessel by using a balloon catheter, the stent mounted on the balloon might be dislocated from a correct mounted position or disengaged from the balloon during insertion. In order to solve this problem, the present inventors have proposed a catheter apparatus to implant a stent in which the stent mounted on a balloon along with the balloon are covered with a proactive sheath and both inserted into a vessel (Patent Document 3).